src/compiler/glsl/loop_analysis.h

   1 /* -*- c++ -*- */
   2 /*
   3  * Copyright © 2010 Intel Corporation
   4  *
   5  * Permission is hereby granted, free of charge, to any person obtaining a
   6  * copy of this software and associated documentation files (the "Software"),
   7  * to deal in the Software without restriction, including without limitation
   8  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   9  * and/or sell copies of the Software, and to permit persons to whom the
  10  * Software is furnished to do so, subject to the following conditions:
  11  *
  12  * The above copyright notice and this permission notice (including the next
  13  * paragraph) shall be included in all copies or substantial portions of the
  14  * Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  22  * DEALINGS IN THE SOFTWARE.
  23  */
  24
  25 #ifndef LOOP_ANALYSIS_H
  26 #define LOOP_ANALYSIS_H
  27
  28 #include "ir.h"
  29 #include "util/hash_table.h"
  30
  31 /**
  32  * Analyze and classify all variables used in all loops in the instruction list
  33  */
  34 extern class loop_state *
  35 analyze_loop_variables(exec_list *instructions);
  36
  37
  38 /**
  39  * Fill in loop control fields
  40  *
  41  * Based on analysis of loop variables, this function tries to remove
  42  * redundant sequences in the loop of the form
  43  *
  44  *  (if (expression bool ...) (break))
  45  *
  46  * For example, if it is provable that one loop exit condition will
  47  * always be satisfied before another, the unnecessary exit condition will be
  48  * removed.
  49  */
  50 extern bool
  51 set_loop_controls(exec_list *instructions, loop_state *ls);
  52
  53
  54 extern bool
  55 unroll_loops(exec_list *instructions, loop_state *ls,
  56              const struct gl_shader_compiler_options *options);
  57
  58
  59 /**
  60  * Tracking for all variables used in a loop
  61  */
  62 class loop_variable_state : public exec_node {
  63 public:
  64    class loop_variable *get(const ir_variable *);
  65    class loop_variable *insert(ir_variable *);
  66    class loop_variable *get_or_insert(ir_variable *, bool in_assignee);
  67    class loop_terminator *insert(ir_if *);
  68
  69
  70    /**
  71     * Variables that have not yet been classified
  72     */
  73    exec_list variables;
  74
  75    /**
  76     * Variables whose values are constant within the body of the loop
  77     *
  78     * This list contains \c loop_variable objects.
  79     */
  80    exec_list constants;
  81
  82    /**
  83     * Induction variables for this loop
  84     *
  85     * This list contains \c loop_variable objects.
  86     */
  87    exec_list induction_variables;
  88
  89    /**
  90     * Simple if-statements that lead to the termination of the loop
  91     *
  92     * This list contains \c loop_terminator objects.
  93     *
  94     * \sa is_loop_terminator
  95     */
  96    exec_list terminators;
  97
  98    /**
  99     * If any of the terminators in \c terminators leads to termination of the
 100     * loop after a constant number of iterations, this is the terminator that
 101     * leads to termination after the smallest number of iterations.  Otherwise
 102     * NULL.
 103     */
 104    loop_terminator *limiting_terminator;
 105
 106    /**
 107     * Hash table containing all variables accessed in this loop
 108     */
 109    hash_table *var_hash;
 110
 111    /**
 112     * Number of ir_loop_jump instructions that operate on this loop
 113     */
 114    unsigned num_loop_jumps;
 115
 116    /**
 117     * Whether this loop contains any function calls.
 118     */
 119    bool contains_calls;
 120
 121    loop_variable_state()
 122    {
 123       this->num_loop_jumps = 0;
 124       this->contains_calls = false;
 125       this->var_hash = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
 126                                                _mesa_key_pointer_equal);
 127       this->limiting_terminator = NULL;
 128    }
 129
 130    ~loop_variable_state()
 131    {
 132       _mesa_hash_table_destroy(this->var_hash, NULL);
 133    }
 134
 135    DECLARE_RALLOC_CXX_OPERATORS(loop_variable_state)
 136 };
 137
 138
 139 class loop_variable : public exec_node {
 140 public:
 141    /** The variable in question. */
 142    ir_variable *var;
 143
 144    /** Is the variable read in the loop before it is written? */
 145    bool read_before_write;
 146
 147    /** Are all variables in the RHS of the assignment loop constants? */
 148    bool rhs_clean;
 149
 150    /**
 151     * Is there an assignment to the variable that is conditional, or inside a
 152     * nested loop?
 153     */
 154    bool conditional_or_nested_assignment;
 155
 156    /** Reference to the first assignment to the variable in the loop body. */
 157    ir_assignment *first_assignment;
 158
 159    /** Number of assignments to the variable in the loop body. */
 160    unsigned num_assignments;
 161
 162    /**
 163     * Increment value for a loop induction variable
 164     *
 165     * If this is a loop induction variable, the amount by which the variable
 166     * is incremented on each iteration through the loop.
 167     *
 168     * If this is not a loop induction variable, NULL.
 169     */
 170    ir_rvalue *increment;
 171
 172
 173    inline bool is_induction_var() const
 174    {
 175       /* Induction variables always have a non-null increment, and vice
 176        * versa.
 177        */
 178       return this->increment != NULL;
 179    }
 180
 181
 182    inline bool is_loop_constant() const
 183    {
 184       const bool is_const = (this->num_assignments == 0)
 185          || (((this->num_assignments == 1)
 186              && !this->conditional_or_nested_assignment
 187              && !this->read_before_write
 188              && this->rhs_clean) || this->var->data.read_only);
 189
 190       /* If the RHS of *the* assignment is clean, then there must be exactly
 191        * one assignment of the variable.
 192        */
 193       assert((this->rhs_clean && (this->num_assignments == 1))
 194              || !this->rhs_clean);
 195
 196       return is_const;
 197    }
 198
 199    void record_reference(bool in_assignee,
 200                          bool in_conditional_code_or_nested_loop,
 201                          ir_assignment *current_assignment);
 202 };
 203
 204
 205 class loop_terminator : public exec_node {
 206 public:
 207    loop_terminator()
 208       : ir(NULL), iterations(-1)
 209    {
 210    }
 211
 212    /**
 213     * Statement which terminates the loop.
 214     */
 215    ir_if *ir;
 216
 217    /**
 218     * The number of iterations after which the terminator is known to
 219     * terminate the loop (if that is a fixed value).  Otherwise -1.
 220     */
 221    int iterations;
 222 };
 223
 224
 225 class loop_state {
 226 public:
 227    ~loop_state();
 228
 229    /**
 230     * Get the loop variable state data for a particular loop
 231     */
 232    loop_variable_state *get(const ir_loop *);
 233
 234    loop_variable_state *insert(ir_loop *ir);
 235
 236    bool loop_found;
 237
 238 private:
 239    loop_state();
 240
 241    /**
 242     * Hash table containing all loops that have been analyzed.
 243     */
 244    hash_table *ht;
 245
 246    void *mem_ctx;
 247
 248    friend loop_state *analyze_loop_variables(exec_list *instructions);
 249 };
 250
 251 #endif /* LOOP_ANALYSIS_H */